that really only applies to people with 1-3 email addresses, where heavy re-use means that any breach likely made it public.

for those with an email address per-service, it's not true at all - and even when an email is leaked it is trivial to shut that email down.

in the past the guidance was don't re-use your passwords - I posit that the guidance should now be don't re-use your email addresses.

Most people with more than 1-3 email address have one account that has a publicly documented form to get unlimited email address. If you use gmail there are two ways to add an alias: the plus sign and adding dots between letters. It is trivial for anyone to check for a plus sign in an email address, and change the part after it thus giving themselves are different alias that you probably don't have blocked. Or they can [email protected] to [email protected].

Because this is so obvious I do not consider email per service useful unless you can cheaply create aliases that are not related to your main email, and adding aliases is not and automatic scheme, but instead. You have to do all of them or the entire scheme is useless, and the effort is high enough that I doubt the average person would do this even if we made it easy. Don't forget that you also need to select the right account to send from for each message while you think the place is not evil.